Efforts to reduce fuel consumption and pollutant emission in modern internal combustion engines should obviously also include the consideration of intermittent or on-off control. With this method, in which individual cylinders are at least temporarily shut off, the mean pressure of the still firing cylinders is raised. This leads to a reduction of the specific fuel consumption. To guarantee that all the cylinders have the operating temperature required for an efficient and low-pollution combustion during intermittent operation, a frequent change-over is necessary between fired and non-fired cylinders.
DE 101 48 179 A1 discloses a valve lift or cam switching arrangement that is suitable for an on-off control of the gas exchange valves of a four-cycle internal combustion engine. This arrangement has the following features and components:                a splined shaft comprising an axial outer gearing and one cam block per cylinder comprising an inner gearing through which the cam block can be axially displaced and connected rotationally fast to the splined shaft;        the cam block comprising per gas exchange valve two cams arranged adjacent to each other and having identical base circle diameters and unequal lifts;        on each end of the cam block is arranged a cylindrical end piece, and a mirror-symmetrical displacing groove is made radially in the periphery of each cylindrical end piece;        a housing-mounted actuator pin for radial insertion into each displacing groove, the cam block being able to reciprocate axially through the cooperation of the actuator pins and the displacing grooves when the engine is running.        
For implementing an on-off control, one full lift cam and one zero lift cam has to be provided for each valve, and these cams are pushed to and fro during change-over between firing and non-firing operation. An intrinsic danger arising from the frequent and rapid switching of the cams is the overloading and wear of the switching mechanism, particularly of the displacing grooves and actuator pins.
Comparable, even if moderated, loading conditions for the displacing grooves and actuator pins are given if the switching-over of the inlet cams of the cam pairs of the cam block serves to realize a two-point camshaft adjuster. To this end, the inlet cams of a cam pair have equal cam lifts but different phases for the range of low and high engine speeds.
In a similar manner, it is possible to conceive a valve train with a fully variable mechanical valve lift adjustment in combination with a cam switching system in which each pair of inlet cams of the cam block comprises one inlet cam that is optimized for low load and speed and one inlet cam that is optimized for high load and speed. In this way, the range of low load and speed can be operated for favorable consumption and the range of high load and speed can be operated for high performance. In both these modes of cam switching, the frequency of switching is low compared to that required in intermittent control.